LTPS TFT Substrate Structure and Method of Forming the Same

ABSTRACT

A method of forming an LTPS TFT substrate includes: Step  1:  providing a substrate ( 1 ) and depositing a buffer layer ( 2 ); Step  2:  depositing an a-Si layer ( 3 ); Step  3:  depositing and patterning a silicon oxide layer ( 4 ); Step  4 : taking the silicon oxide layer ( 4 ) as a photomask and annealing the a-Si layer ( 3 ) with excimer laser, so that the a-Si layer crystalizes and turns into a poly-Si layer; Step  5:  forming a first poly-Si region ( 31 ) and a second poly-Si region ( 32 ); Step  6:  defining a heavily N-doped area and a lightly N-doped area on the first and second poly-Si regions ( 31 ) and ( 32 ), and forming an LDD area; Step  7:  depositing and patterning a gate insulating layer ( 5 ); Step  8:  forming a first gate ( 61 ) and a second gate ( 62 ); Step  9:  forming via holes ( 70 ); and Step  10:  forming a first source/drain ( 81 ) and a second source/drain ( 82 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to display technology, and more specifically, to a low temperature poly-silicon (LTPS) thin-film transistor (TFT) substrate structure and a method of forming the same.

2. Description of the Prior Art

Thin-film transistor liquid crystal display (TFT-LCD) can be achieved by two approaches: polycrystalline silicon (poly-Si) and amorphous silicon (a-Si). Low temperature poly-silicon (LTPS) is the latest generation of TFT-LCD producing technology. The biggest different between a LTPS TFT-LCD and a conventional a-Si TFT-LCD is that the former responds faster, has higher brightness and resolution, and consumes less power.

The crystalline silicons used by LTPS technology are arrayed more orderly than that used by a-Si technology. Therefore, the electron mobility of LTPS technology is over 100 times higher than that of a-Si technology. The peripheral driver can be built on the same glass substrate, saving space and the cost of driver integrated circuit (IC). Because the driver IC is directly built on the substrate, it reduces the number of external contact points, increases reliability, simplifies maintenance procedure, shortens assembly time, and lowers electromagnetic interference, which shortens the time needed for application system design, and renders more flexibility in design.

FIG. 1 is a diagram of a conventional LTPS TFT substrate. The forming method generally comprises the following steps:

Step 1: Provide a substrate 100 and deposit a buffer layer 200;

Step 2: Deposit an a-Si layer on the buffer layer 200;

Step 3: Anneal the a-Si layer with excimer laser, so that the a-Si layer is turned into a poly-Si layer.

Step 4: Pattern the poly-Si layer through lithography and etching process so to form a first poly-Si region 310 in the display area, and a second poly-Si region 320 in the drive area. These two regions are arrayed with a space in between.

Step 5: Define a heavily N-doped area and lightly N-doped area on the first poly-Si region 310 and the second poly-Si region 320 respectively. Implant different dosages of P31 in the heavily N-doped area and lightly N-doped area so to form lightly doped drain (LDD) areas.

Step 6: Deposit and pattern a gate insulating layer 500 on the buffer layer 2, the first poly-Si region 310 and the second poly-Si region 320.

Step 7: Deposit and pattern a first metal layer on the gate insulating layer 500 corresponding to the first poly-Si region 310 and the second poly-Si region 320 to form a first gate 610 and a second gate 620.

Step 8: Form an interlayer dieletric (ILD) layer 700 on the gate insulating layer 500. Form via holes 710 leading to the heavily N-doped areas next to the first poly-Si region 310 and the second poly-Si region 320 through the gate insulating layer 500 and the interlayer dieletric layer 700.

Step 9: Deposit and pattern a second metal layer on top of the interlayer dieletric layer 700 to form a first source/drain 810 and a second source/drain 820.

The first source/drain 810 and the second source/drain 820 are in contact with the heavily N-doped areas next to the first poly-Si region 310 and the second poly-Si region 320 through the via hole 710. And then, a complete LTPS TFT substrate is formed through subsequent standard procedure.

A LTPS TFT substrate comprises a display area, and a drive area located in a non-display area. The conventional forming method of the LTPS TFTs results in poorer uniformity in the display area, and lower-than-expected electron mobility of the driver in the drive area, further affecting the quality of LTPS TFT substrates.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of forming a LTPS TFT substrate that has relatively larger poly-Si dies and attains to higher electron mobility in the drive area, so to elevate the electrical characteristics of the driver. On the other hand, it has relatively smaller poly-Si dies with better uniformity in the display area, so that the electrical property of the TFT within the display area can be more even, and the quality of the LTPS TFT substrate is improved.

Another object of the present invention is to provide a LTPS TFT substrate structure with its poly-Si region in the drive area producing larger poly-Si dies and poly-Si region in the display area producing smaller poly-Si dies with better uniformity. Thus the drive has better electrical characteristics, and the TFT in the display area has more uniformed electrical property, so that the TFT substrate will have higher quality.

According to the present invention, a method of forming a low temperature poly-Si (LTPS) thin-film transistor (TFT) substrate, comprises:

Step 1: providing a substrate and depositing a buffer layer on the substrate;

Step 2: depositing an a-Si layer on the buffer layer;

Step 3: depositing a silicon oxide layer on the a-Si layer, and patterning the silicon oxide layer through lithography and etching process, so to form a silicon oxide layer in the display area;

Step 4: taking the silicon oxide layer as a photomask and annealing the a-Si layer with excimer laser, so that the a-Si layer crystalizes and turns into a poly-Si layer, and removing the silicon oxide layer;

Step 5: patterning the poly-Si layer through lithography and etching process so to form a first poly-Si region in the display area, and a second poly-Si region in the drive area, with the two regions arrayed with a space in between;

Step 6: defining a heavily N-doped area and a lightly N-doped area on the first and second poly-Si regions respectively, and implanting different dosages of P31 into the heavily N-doped area and the lightly N-doped area, so to form a lightly doped drain (LDD) area;

Step 7: depositing and patterning a gate insulating layer on the buffer layer, the first and the second poly-Si regions;

Step 8: depositing a first metal layer on the gate insulating layer, and patterning the metal layer to form a first gate and a second gate corresponding to the first and the second poly-Si regions respectively;

Step 9: forming an interlayer dieletric layer on the gate insulating layer, and forming via hole leading to the heavily N-doped areas next to the first and second poly-Si regions through the gate insulating layer and the interlayer dieletric layer;

Step 10: depositing and patterning a second metal layer on the interlayer dieletric layer, and forming a first source/drain and a second source/drain;

with the first source/drain and the second source/drain connecting to the heavily N-doped areas next to the first and second poly-Si regions through the via hole.

In one aspect of the present invention, materials of the buffer layer are either silicon nitride, silicon oxide, or the combination of both.

In another aspect of the present invention, materials of the interlayer dieletric layer are either silicon oxide, silicon nitride, or the combination of both.

In still another aspect of the present invention, each of the first gate and the second gate is a single layer or stacked layers, and each layer is made of a material selected from molybdenum, titanium, aluminum, or copper.

In still another aspect of the present invention, in the Step 6, the heavily N-doped area and the lightly N-doped area are defined by applying lithographic photoresist and two photomasks respectively, and lightly doped drain areas are produced by implanting different dosages of P31 in the heavily N-doped area and lightly N-doped area.

In yet another aspect of the present invention, the gate insulating layer, the first gate, the second gate, the via hole, the first source/drain and the second source/drain are formed through deposition, lithography and etching process.

According to the present invention, a LTPS TFT substrate comprises: a substrate; a buffer layer on the substrate; a first poly-Si region and a second poly-Si region arrayed on the buffer layer with a space between the two regions; a first source/drain and a second source/drain disposed above the first poly-Si region and the second poly-Si region; a gate insulating layer installed on the buffer layer, the first poly-Si region and second poly-Si region; a first gate and a second gate installed on the gate insulating layer corresponding to the first poly-Si region and second poly-Si region; an interlayer dieletric layer installed on the gate insulating layer, the first gate and the second gate. Both sides of the first poly-Si region and the second poly-Si region are next to a heavily N-doped area, which connects to the first source/drain and the second source/drain through the via hole.

The LTPS TFT substrate further comprises a display area and a drive area, with the first poly-Si region in the display area of the LTPS TFT substrate, and the second poly-Si region in the drive area of the LTPS TFT substrate. The dies of the first poly-Si region is smaller than that of the second poly-Si region, while the uniformity of the dies of the first poly-Si region is larger than that of the second poly-Si region.

In one aspect of the present invention, materials of the buffer layer are either silicon nitride, silicon oxide, or a combination of both.

In another aspect of the present invention, materials of the interlayer dieletric layer are silicon oxide, silicon nitride, or a combination of both.

In still another aspect of the present invention, each of the first gate and the second gate is a single layer or stacked layers, and each layer is made of a material selected from molybdenum, titanium, aluminum, or copper.

According to the present invention, a LTPS TFT substrate comprises: a substrate; a buffer layer on the substrate; a first poly-Si region and a second poly-Si region arrayed on the buffer layer with a space between the two regions; a first source/drain and a second source/drain disposed above the first poly-Si region and the second poly-Si region; a gate insulating layer installed on the buffer layer, the first poly-Si region and second poly-Si region; a first gate and a second gate installed on the gate insulating layer corresponding to the first poly-Si region and second poly-Si region; an interlayer dieletric layer installed on the gate insulating layer, the first gate and the second gate. Both sides of the first poly-Si region and the second poly-Si region are next to a heavily N-doped area, which connects to the first source/drain and the second source/drain through the via hole.

The LTPS TFT substrate further comprises a display area and a drive area, with the first poly-Si region in the display area of the LTPS TFT substrate, and the second poly-Si region in the drive area of the LTPS TFT substrate. The dies of the first poly-Si region is smaller than that of the second poly-Si region, while the uniformity of the dies of the first poly-Si region is larger than that of the second poly-Si region.

wherein materials of the buffer layer are either silicon nitride, silicon oxide, or a combination of both.

wherein materials of the interlayer dieletric layer are silicon oxide, silicon nitride, or a combination of both.

wherein each of the first gate and the second gate is a single layer or stacked layers, and each layer is made of a material selected from molybdenum, titanium, aluminum, or copper.

The present invention brings several benefits. The forming method of the LTPS TFT substrate of the present invention first deposits and patterns a layer of silicon oxide on the a-Si layer, producing a layer of silicon oxide on the a-Si layer in the display area. Then, the silicon oxide layer serves as a photomask when the a-Si layer is annealed by excimer laser and crystalizes, and turns into a poly-Si layer. It forms relatively larger dies in the drive area and attains to higher electron mobility. The display area, because of the shielding of the silicon oxide layer, is exposed to lower laser energy, thus forms relatively smaller dies with better uniformity. It ensures a more even electron mobility in the display area and enhances the quality of the LTPS TFT substrate. The forming process is simple and easy to operate. In addition, the present invention provides a LTPS TFT substrate structure with poly-Si regions in the drive area producing larger dies than in the display area, so to ensure that the drive has better electrical characteristics and the TFT within the display area has more even electrical property. The TFT substrate, therefore, has better quality.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification.

FIG. 1 shows a structure diagram of a conventional LTPS TFT substrate.

FIG. 2 shows a flowchart of a method for forming a LTPS TFT substrate according to a preferred embodiment of the present invention.

FIG. 3 shows a diagram of a step 1 of the method for forming the LTPS TFT substrate as depicted in FIG. 2.

FIG. 4 shows a diagram of a step 2 of the method for forming the LTPS TFT substrate as depicted in FIG. 2.

FIG. 5 shows a diagram of a step 3 of the method for forming the LTPS TFT substrate as depicted in FIG. 2.

FIGS. 6-7 show a diagram of a step 4 of the method for forming the LTPS TFT substrate as depicted in FIG. 2.

FIG. 8 shows a diagram of a step 5 of the method for forming the LTPS TFT substrate as depicted in FIG. 2.

FIG. 9 shows a diagram of a step 6 of the method for forming the LTPS TFT substrate as depicted in FIG. 2.

FIG. 10 shows a diagram of a step 7 of the method for forming the LTPS TFT substrate as depicted in FIG. 2.

FIG. 11 shows a diagram of a step 8 of the method for forming the LTPS TFT substrate as depicted in FIG. 2.

FIG. 12 shows a diagram of a step 9 of the method for forming the LTPS TFT substrate as depicted in FIG. 2.

FIG. 13 shows a diagram of a step 10 of the method for forming the LTPS TFT substrate as depicted in FIG. 2, and a cross-sectional view of the LTPS TFT substrate according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

Please refer to FIG. 1. The present invention provides a method of forming a LTPS TFT substrate comprising the following steps:

Step 1: Provide a substrate 1, and deposit a buffer layer 2 on the substrate 1, as shown in FIG. 3.

The substrate 1 is a transparent substrate which is made, preferably, of glass or plastic.

Specifically, the materials of the buffer layer 2 can be either silicon nitride (SiNx), silicon oxide (SiOx), or the combination of the two.

Step 2: Deposit an a-Si layer 3 on the buffer layer 2, as shown in FIG. 4.

Step 3: As shown in FIG. 5, deposit a silicon oxide layer on the a-Si layer 3, and pattern the silicon oxide layer through lithography and etching process so to get a silicon oxide layer 4 in the display area. The a-Si layer 3 in the drive area of the non-display area, at this stage, is not covered by the silicon oxide layer 4.

Step 4: As shown in FIGS. 6 and 7, the silicon oxide layer 4 is taken as a photomask when the a-Si layer 3 is annealed by excimer laser. The a-Si layer 3 thus crystalizes and turns into a poly-Si layer, and the silicon oxide layer 4 is removed.

When the a-Si layer 3 is annealed by excimer laser, the part in the display area is exposed to relatively lower laser energy as it is covered by the silicon oxide layer 4, so dies formed in this part are smaller but with better uniformity. The a-Si layer 3 in the drive area is not covered by the silicon oxide layer 4, therefore it is exposed to higher laser energy and forms relatively larger dies.

Step 5: As shown in FIG. 8, a first poly-Si region 31 in the display area and a second poly-Si region 32 in the drive area are formed by patterning the poly-Si layer through lithography and etching process. The first poly-Si region 31 and the second poly-Si region 32 are arrayed with a space in between.

The first poly-Si region 31 in the display area has smaller dies with better uniformity, whereas the second poly-Si region 32 in the drive area has larger dies.

Step 6: As shown in FIG. 9, a heavily N-doped area and lightly N-doped area are defined respectively on the first poly-Si region 31 and the second poly-Si region 32. Different dosages of P31 (Phosphorus-31) are implanted in the heavily N-doped area and lightly N-doped area respectively to form LDD areas.

Specifically, the heavily N-doped area and the lightly N-doped area are defined by applying lithographic photoresist and two photomasks, respectively. Implant different dosages of P31 (Phosphorus-31) in the heavily N-doped area and lightly N-doped area, so to form LDD areas.

Step 7: As shown in FIG. 10, deposit and pattern a gate insulating layer 5 on the buffer layer 2, the first poly-Si region 31 and the second poly-Si region 32.

Step 8: As shown in FIG. 11, deposit and pattern a first metal layer and form a first gate 61 and a second gate 62 on the gate insulating layer 5 corresponding to the first poly-Si region 31 and the second poly-Si region 32.

Specifically, each of the first gate 61 and the second gate 62 is a single layer or stacked layers, and each layer is made of a material selected from molybdenum (Mo), titanium (Ti), aluminum (Al) or copper (Cu).

Step 9: As shown in FIG. 12, form an interlayer dieletric layer 7 on the gate insulating layer 5. Form via holes 70 leading to the heavily N-doped areas next to the first poly-Si region 31 and the second poly-Si region 32 through the gate insulating layer 5 and the interlayer dieletric layer 7.

Specifically, materials of the interlayer dieletric layer 7 can be silicon nitride (SiNx), silicon oxide (SiOx), or a combination of both.

Step 10: As shown in FIG. 13, deposit and pattern a second metal layer on the interlayer dieletric layer 7, so to form a first source/drain 81 and a second source/drain 82.

The first source/drain 81 and the second source/drain 82 contacts the heavily N-doped areas next to the first poly-Si region 31 and the second poly-Si region 32 respectively through the via holes 70. The existing techniques can be applied afterwards so to complete the following procedure, and eventually produce a LTPS TFT substrate.

Specifically, the gate insulating layer 5, the first gate 61, the second gate 62, the via hole 70, and the first source/drain 81 and the second source/drain 82 are formed through deposition, lithography and etching process.

The method of forming the LTPS TFT substrate deposits and patterns a layer of silicon oxide on the a-Si layer first, and then anneals the a-Si layer with excimer laser, so to get a silicon oxide layer on the a-Si layer in the display area. Then, the silicon oxide layer serves as a photomask when the a-Si layer is annealed by excimer laser and crystalizes, and turns into a poly-Si layer. It forms larger dies in the drive area and has better electron mobility. The display area is exposed to lower laser energy as it is shielded by the silicon oxide layer, thus it forms relatively smaller dies with better uniformity. Therefore, the electron mobility in the display area has better uniformity and thus elevates the quality of the LTPS TFT substrate.

Please refer to FIG. 13. The present invention further provides a LTPS TFT substrate structure, comprising a substrate 1; a buffer layer 2 on the substrate 1; a first poly-Si region 31 and a second poly-Si region 32 arrayed with a space in between on the buffer layer 2; a first source/drain 81 and a second source/drain 82 disposed above the first poly-Si region 31 and second poly-Si region 32; a gate insulating layer 5 installed on the buffer layer 2, the first poly-Si region 31 and second poly-Si region 32; a first gate 61 and a second gate 62 installed on the gate insulating layer 5 corresponding to the first poly-Si region 31 and second poly-Si region 32; and an interlayer dieletric layer 7 installed on the gate insulating layer 5, the first gate 61 and the second gate 62. Both sides of the first poly-Si region 31 and second poly-Si region 32 are next to a heavily N-doped area, which are connected to the first source/drain 81 and the second source/drain 82 through via holes 70.

The LTPS TFT substrate comprises a display area and a drive area. The first poly-Si region 31 is in the display area of the LTPS TFT substrate, and the second poly-Si region 32 is in the drive area of the LTPS TFT substrate. The dies of the first poly-Si region 31 is smaller than that of the second poly-Si region 32, yet the uniformity of the dies of the first poly-Si region 31 is larger than that of the second poly-Si region 32.

A substrate 1 is a transparent substrate which is made, preferably, of glass or plastic.

Specifically, materials of the buffer layer 2 and the interlayer dieletric layer 7 can be either silicon nitride (SiNx), silicon oxide (SiOx), or the combination of the two.

Each of the first gate 61 and the second gate 62 is a single layer or stacked layers, and each layer is made of a material selected from molybdenum (Mo), titanium (Ti), aluminum (Al) or copper (Cu).

The dies of the poly-Si region of the present LTPS TFT structure is larger in the drive area than in the display area, but has better uniformity in the display area than in the drive area. Therefore the drive has better electrical characteristics, and the TFT within the display area has more even electrical property, so that the TFT substrate has better quality.

In Sum, the forming method of the LTPS TFT substrate of the present invention proposes depositing and patterning a layer of silicon oxide on the a-Si layer, producing a layer of silicon oxide on the a-Si layer in the display area. Then, the silicon oxide layer serves as a photomask when the a-Si layer is annealed by excimer laser and crystalizes, and turns into a poly-Si layer. It forms relatively larger dies in the drive area and attains to higher electron mobility. The display area, because of the shielding of the silicon oxide layer, is exposed to lower laser energy, thus forms relatively smaller dies with better uniformity. It ensures a more even electron mobility in the display area and enhances the quality of the LTPS TFT substrate. The forming process is simple and easy to operate. In addition, the present invention provides a LTPS TFT substrate structure with poly-Si regions in the drive area producing larger dies than in the display area, so to ensure that the drive has better electrical characteristics and the TFT within the display area has more even electrical property. The TFT substrate, therefore, has better quality.

While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements made without departing from the scope of the broadest interpretation of the appended claims. 

What is claimed is:
 1. A method of forming a low temperature poly-Si (LTPS) thin-film transistor (TFT) substrate, comprising: Step 1: providing a substrate and depositing a buffer layer on the substrate; Step 2: depositing an a-Si layer on the buffer layer; Step 3: depositing a silicon oxide layer on the a-Si layer, and patterning the silicon oxide layer through lithography and etching process, so to form a silicon oxide layer in the display area; Step 4: taking the silicon oxide layer as a photomask and annealing the a-Si layer with excimer laser, so that the a-Si layer crystalizes and turns into a poly-Si layer, and removing the silicon oxide layer; Step 5: patterning the poly-Si layer through lithography and etching process so to form a first poly-Si region in the display area, and a second poly-Si region in the drive area, with the two regions arrayed with a space in between; Step 6: defining a heavily N-doped area and a lightly N-doped area on the first and second poly-Si regions respectively, and implanting different dosages of P31 into the heavily N-doped area and the lightly N-doped area, so to form a lightly doped drain (LDD) area; Step 7: depositing and patterning a gate insulating layer on the buffer layer, the first and the second poly-Si regions; Step 8: depositing a first metal layer on the gate insulating layer, and patterning the metal layer to form a first gate and a second gate corresponding to the first and the second poly-Si regions respectively; Step 9: forming an interlayer dieletric layer on the gate insulating layer, and forming via hole leading to the heavily N-doped areas next to the first and second poly-Si regions through the gate insulating layer and the interlayer dieletric layer; Step 10: depositing and patterning a second metal layer on the interlayer dieletric layer, and forming a first source/drain and a second source/drain; with the first source/drain and the second source/drain connecting to the heavily N-doped areas next to the first and second poly-Si regions through the via hole.
 2. The method of claim 1, wherein materials of the buffer layer are either silicon nitride, silicon oxide, or the combination of both.
 3. The method of claim 1, wherein materials of the interlayer dieletric layer are either silicon oxide, silicon nitride, or the combination of both.
 4. The method of claim 1, wherein each of the first gate and the second gate is a single layer or stacked layers, and each layer is made of a material selected from molybdenum, titanium, aluminum, or copper.
 5. The method of claim 1, wherein in the Step 6, the heavily N-doped area and the lightly N-doped area are defined by applying lithographic photoresist and two photomasks respectively, and lightly doped drain areas are produced by implanting different dosages of P31 in the heavily N-doped area and lightly N-doped area.
 6. The method of claim 1, wherein the gate insulating layer, the first gate, the second gate, the via hole, the first source/drain and the second source/drain are formed through deposition, lithography and etching process.
 7. A LTPS TFT substrate, comprising: a substrate; a buffer layer on the substrate; a first poly-Si region and a second poly-Si region arrayed on the buffer layer with a space between the two regions; a first source/drain and a second source/drain disposed above the first poly-Si region and the second poly-Si region; a gate insulating layer installed on the buffer layer, the first poly-Si region and second poly-Si region; a first gate and a second gate installed on the gate insulating layer corresponding to the first poly-Si region and second poly-Si region; an interlayer dieletric layer installed on the gate insulating layer, the first gate and the second gate; wherein both sides of the first poly-Si region and the second poly-Si region are next to a heavily N-doped area, which connects to the first source/drain and the second source/drain through the via hole; a display area and a drive area, with the first poly-Si region in the display area of the LTPS TFT substrate, and the second poly-Si region in the drive area of the LTPS TFT substrate; the dies of the first poly-Si region is smaller than that of the second poly-Si region, while the uniformity of the dies of the first poly-Si region is larger than that of the second poly-Si region.
 8. The LTPS TFT substrate of claim 7, wherein materials of the buffer layer are either silicon nitride, silicon oxide, or a combination of both.
 9. The LTPS TFT substrate of claim 7, wherein materials of the interlayer dieletric layer are silicon oxide, silicon nitride, or a combination of both.
 10. The LTPS TFT substrate of claim 7, wherein each of the first gate and the second gate is a single layer or stacked layers, and each layer is made of a material selected from molybdenum, titanium, aluminum, or copper.
 11. A LTPS TFT substrate, comprising: a substrate; a buffer layer on the substrate; a first poly-Si region and a second poly-Si region arrayed on the buffer layer with a space between the two regions; a first source/drain and a second source/drain disposed above the first poly-Si region and the second poly-Si region; a gate insulating layer installed on the buffer layer, the first poly-Si region and second poly-Si region; a first gate and a second gate installed on the gate insulating layer corresponding to the first poly-Si region and second poly-Si region; an interlayer dieletric layer installed on the gate insulating layer, the first gate and the second gate; wherein both sides of the first poly-Si region and the second poly-Si region are next to a heavily N-doped area, which connects to the first source/drain and the second source/drain through the via hole; a display area and a drive area, with the first poly-Si region in the display area of the LTPS TFT substrate, and the second poly-Si region in the drive area of the LTPS TFT substrate; the dies of the first poly-Si region is smaller than that of the second poly-Si region, while the uniformity of the dies of the first poly-Si region is larger than that of the second poly-Si region; wherein materials of the buffer layer are either silicon nitride, silicon oxide, or a combination of both; wherein materials of the interlayer dieletric layer are silicon oxide, silicon nitride, or a combination of both; wherein each of the first gate and the second gate is a single layer or stacked layers, and each layer is made of a material selected from molybdenum, titanium, aluminum, or copper. 